1. Field of the Invention
The present invention relates to an inflator for an inflatable air bag, and more particularly, to such an inflator having a thin-walled hermetic liner, filled with stored gas, with a minimal number of joints required to be sealed.
2. Description of the Related Art
An inflatable air bag is a safety device for protecting automotive vehicle occupants in a collision. When a sensor discerns an imminent collision and the need for inflation of the air bag, an initiator is fired. This releases gas under high pressure from an inflator into the air bag which is initially folded. The air bag expands and provides a protective cushion that restrains the driver or passenger against various impact conditions.
Many types of inflators have been disclosed in the art for use in an inflatable restraint system. One involves the utilization of a quantity of stored compressed gas which is released at the stored temperature to inflate the air bag. Another derives a gas source from a combustible gas generating material which, upon ignition, generates a quantity of hot gas sufficient to inflate the air bag. In a third type, the air bag inflating gas results from a combination of stored compressed inert gas and a gas generating material. The last mentioned type, commonly referred to as an augmented gas or hybrid inflator, delivers hot gas to the air bag.
As noted in U.S. Pat. No. 3,756,621 granted to Donald J. Lewis, et al., on Sep. 4, 1973, the use of a quantity of compressed argon, an inert gas, is advantageous. Compressed air and compressed nitrogen have specific problems related to their use. Air is not inert and when compressed to relatively high pressure becomes a source of significant hazard. Nitrogen is relatively inert when compressed but contributes to the production of nitrogen oxide and nitrogen dioxide especially when intermixed with hot gases generated by combustible materials.
The inflator may comprise a quantity of inert gas under high pressure in a storage cylinder or bottle. An advantage accrues, however, where a stored compressed gas augmented by a generated gas is utilized. This advantage involves the addition of energy to the stored compressed gas to aid in filling the air bag. Current technology with hybrid inflators to obtain this advantage is to heat the stored high pressure gas with some type of pyrotechnic. Such hybrid inflators, however, are subject to a disadvantage, even when argon is used as the stored compressed gas, because the gas delivered to the air bag is hot and is mixed with a gas produced by combustion of the pyrotechnic. Such systems fill air bags with some types of gases, particulates or smoke that can be irritating or noxious to occupants of a vehicle.
In a recent improvement in hybrid inflator technology, as disclosed in U.S. Pat. No. 5,301,979 that on Apr. 12, 1994 was granted to John E. Allard and assigned to the assignee of the present invention, cold pressurized pure inert gas (i.e., argon, nitrogen) is delivered to an air bag by an inflator with the addition of mechanical energy instead of heat energy. The inflator comprises a high strength container having a cylindrical section that is filled with the inert gas. A piston is located at one end of the cylindrical section with a high energy pyrotechnic behind it. During storage both sides of the piston are at the same pressure. An initiator is located in the high energy pyrotechnic. A burst disk is located at the opposite end of the cylindrical section. When the initiator is fired, the piston is driven down the length of the cylindrical section. When the pressure in the container exceeds the burst disk strength, the pure inert gas expands in a blow down manner into the air bag. There is no intermixture of gases or particulates produced by the pyrotechnic.
In order to ensure operability over ten (10) or more years, the life of the vehicle in which it is installed, the container of the pressurized pure gas inflator of the Allard patent must be hermetically sealed. Also, the rate at which the air bag is filled is slower and less controllable than desirable for some purposes.
There is a need and a demand for improvement in inflators to the end of providing a simpler, less expensive assembly process and the creation of an inflator that will fill the air bag quicker than a cold gas or blow down system of the same size and pressure, wherein the production of unwanted gaseous products of combustion are eliminated, and virtually no particulate matter is produced.
A rather comprehensive disclosure regarding fluid-filled inflators is disclosed in application Ser. No. 08/252036 filed in the U.S. Patent and Trademark Office on May 31, 1994 by Karl Rink and Bradley W. Smith entitled "FLUID FUELED AIR BAG INFLATOR" and assigned to the assignee of the present invention. This disclosure comprises an apparatus and method for inflating a vehicular inflatable device that is adaptable to a variety of fuels and oxidants wherein a fluid fuel is burned and mixed with stored, pressurized gas to produce inflation gas containing little or no particulate.